A selective differential medium for the isolation of Listeria monocytogenes

A new medium has been developed for the isolation of Listeria monocytogenes from clinical specimens with a mixed flora. Almost complete inhibition of unwanted organisms was achieved and recognition of colonies of Listeria spp. was usually possible after 24 h using the aesculin-ferric ammonium citrate indicator system. Compared to McBride agar the new medium was more inhibitory to representative contaminating species in pure culture and more successful in isolating small numbers of L. monocytogenes from artificially seeded clinical specimens.     

Highly selective medium for isolation of Listeria monocytogenes from food

A new selective medium (Al-Zoreky-Sandine listeria medium [ASLM]) was formulated to recover Listeria monocytogenes from food specimens; the medium completely inhibited common food microflora. Recognition of Listeria colonies is evident by black discoloration of the medium due to esculin hydrolysis without need for special illuminating equipment. The medium contains acriflavin, ceftazidime, and moxalactam as selective agents. Compared with Listeria Selective Agar, ASLM was equally effective in recovering L. monocytogenes. However, ASLM inhibited micrococci, enterococci, and gram-negative bacteria, especially a strain that mimicked L. monocytogenes on Listeria Selective Agar. The new medium was able to recover heat injured cells with only 15% less count than the nonselective medium.     

Highly selective medium for isolation of Listeria monocytogenes from food.

A new selective medium (Al-Zoreky-Sandine listeria medium [ASLM]) was formulated to recover Listeria monocytogenes from food specimens; the medium completely inhibited common food microflora. Recognition of Listeria colonies is evident by black discoloration of the medium due to esculin hydrolysis without need for special illuminating equipment. The medium contains acriflavin, ceftazidime, and moxalactam as selective agents. Compared with Listeria Selective Agar, ASLM was equally effective in recovering L. monocytogenes. However, ASLM inhibited micrococci, enterococci, and gram-negative bacteria, especially a strain that mimicked L. monocytogenes on Listeria Selective Agar. The new medium was able to recover heat injured cells with only 15% less count than the nonselective medium.     

An improved selective isolation medium for the recovery of Listeria monocytogenes from smoked fish

AIMS: The aim of this study was to improve the selective isolation of Listeria monocytogenes from smoked haddock fillets. METHODS AND RESULTS: Listeria selective agar (LSA)--Oxford formulation was supplemented with 25 microg x ml(-1) of colistin sulphate and 30 microg x ml(-1) of nalidixic acid. Inocula from four smoked haddock fillets produced colonies (approx. 2-13 bacteria x g(-1)), identified as L. monocytogenes, on LSA supplemented with antimicrobial compounds (MLSA). Moreover, there was only negligible evidence of bacteria which were not L. monocytogenes on MLSA. In contrast, LSA supported dense bacterial growth, which was not equated with L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: The modified medium permitted the recovery of L. monocytogenes from smoked haddock fillets and reduced the growth of contaminating bacteria.     

A new selective, differential agar medium for isolation of Vibrio cholerae O1: PMT (polymyxin-mannose-tellurite) agar

A new selective and differential agar medium, polymyxin-mannose-tellurite (PMT) agar was devised to differentiate easily colonies of Vibrio cholerae O1 from those of V. cholerae non-O1. The differentiation between colonies of the two vibrios is based on mannose-fermentation. Colonies of V. cholerae O1 on the agar are agglutinated with O1 antiserum of V. cholerae much more easily than those on thiosulfate-citrate-bile salts-sucrose (TCBS) agar.     

Evaluation of enhanced haemolysis agar for detection of Listeria spp. and L. monocytogenes from production lines of fresh to cold-smoked fish.

Enhanced haemolysis agar (EHA) was compared to the two conventional Listeria isolation agars Oxford and PALCAM for its ability to detect Listeria spp. from production lines of fresh to cold-smoked fish. The ability of EHA for distinguishing L. monocytogenes colonies from other Listeria spp. was also evaluated.A total of 243 fish and environmental samples were analysed. Overall, 42 samples were found to contain Listeria spp. Only 34 samples were positive simultaneously by the three plating media. Two samples considered to be negative by the two conventional agars were found to be positive after isolation on EHA. All three selective agars were shown to be less effective in recovering Listeria spp. after primary enrichment in half-Fraser broth, compared to secondary enrichment in Fraser broth after 24 and 48 h.From 79 Listeria but presumptive negative L. monocytogenes colonies, EHA identified correctly 76 Listeria spp. and presented three false-negative results_three colonies further identified as L. monocytogenes but showing no noticeable haemolysis on EHA. Twenty-three of the thirty-three L. monocytogenes presumptive positive colonies, were confirmed positive and ten were identified as L. seeligeri.Despite its ability of distinguishing L. monocytogenes from the other Listeria spp., unless it is produced as a commercial medium, EHA cannot be an alternative to time-consuming classical identification because the preparation of this medium is both time and labour intensive.     

Evaluation of BBL CHROMagar Listeria agar for the isolation and identification of Listeria monocytogenes from food and environmental samples

The performance of BBL CHROMagar Listeria chromogenic agar for the detection of Listeria monocytogenes was evaluated for its ability to isolate and identify L. monocytogenes from food and environmental samples. The medium was compared to non-chromogenic selective agars commonly used for Listeria isolation: Oxford, Modified Oxford, and PALCAM. BBL CHROMagar Listeria had a sensitivity of 99% and 100% for the detection of L. monocytogenes from 200 natural and artificially inoculated food samples, respectively, with a colony confirmation rate of 100%. The sensitivity of non-chromogenic selective media for the detection of L. monocytogenes from these same samples was 97-99% with colony confirmation rates of 65-67.5%. From 93 environmental samples, BBL CHROMagar Listeria agar results correlated 100% with a Listeria spp. visual immunoassay (TECRA) performed on these same samples and the USDA-FSIS standard culture method for the isolation of L. monocytogenes. From environmental samples, the L. monocytogenes confirmation rate was 100% for BBL CHROMagar Listeria as compared to 50% for conventional agars tested. On BBL CHROMagar Listeria, L. monocytogenes forms a translucent white precipitation zone (halo) surrounding blue-pigmented colonies of 2-3 mm in diameter, with an entire border. BBL CHROMagar Listeria offers a high degree of specificity for the confirmation of suspect L. monocytogenes colonies, whereas non-chromogenic selective agars evaluated were not differential for L. monocytogenes from other Listeria species.     

Development of an improved selective agar medium for isolation of Yersinia pestis

Existing media designed for selective isolation of clinically important members of the genus Yersinia were found to be unsatisfactory for the growth and isolation of Yersinia pestis. We report the development of a new selective agar medium (termed BIN) that supports the growth of Y. pestis. The development of the formulation of this medium was based on a fluorescence screening system designed for monitoring bacterial growth on semisolid media, using a green fluorescent protein-expressing strain. High-throughput combinatorial experiments can be conducted for the quantitative evaluation of the effect of different medium components on growth. Generation of fluorescence plots in this system, using microplates, allowed the quantitative evaluation of the growth rate of Y. pestis EV76 cultures in different agar compositions. The final BIN formulation is based on brain heart infusion agar, to which the selective agents irgasan, cholate salts, crystal violet, and nystatin were introduced. It was found that BIN agar is more efficient in supporting colony formation and recovery of Y. pestis than are the conventional semisolid media MacConkey agar and Yersinia-selective agar (cefsulodin-irgasan-novobiocin agar). The advantage of BIN over other media has been also demonstrated in recovering virulent Y. pestis from the mixed bacterial populations found in decaying carcasses of infected mice. The BIN medium is suggested as a selective medium for isolation and recovery of Y. pestis from various backgrounds.     

Development of a selective myclobutanil agar (MBA) medium for the isolation of Fusarium species from asparagus fields

A new selective myclobutanil agar medium for the detection of Fusarium, species is proposed. Ten media formulations based on various selective agents (pentachloronitrobenzene (PCNB), Rose Bengal, malachite green, sodium hypochlorite, captan, benomyl, chlorotalonil, myclobutanil, thiram, and cupric sulfate) were compared. First, mycelium growth and colony appearance of Alternaria alternata, Aspergillus flavus, Cladosporium cladosporioides, Epicoccum nigrum, Fusarium sp., Fuisarium solani, Fusarium moniliforme, Fusarium oxysporum f.sp. dianthi, Penicillium sp., and Trichoderma viride isolates were compared. Second, the ability of the different media to isolate and enumerate fusaria from asparagus fields was evaluated. The myclobutanil-based medium showed the highest selectivity to Fusarium spp. growth but required a slightly longer incubation time (>5 d) than peptone-pentachloronitrobenzene-based agar (PPA) (< 5 d). PPA allowed a faster fusaria growth but also permited the growth of other moulds. The other media were less selective and did not allow to isolate fusaria or to differenciate them from other growing fungi.     

Humic acid-vitamin agar,a new medium for the selective isolation of soil actinomycetes

A new medium, designated HV agar, containing soil humic acid as the sole source of carbon and nitrogen was developed.The HV agar was superior to other currently used media, including colloidal chitin agar, glycerol-arginine agar and starch-casein-nitrate agar, for the isolation and enumeration of soil actinomycetes: It allowed the growth of the largest numbers of actinomycete colonies belonging to each genus of Streptomyces, Micromonospora, Microbispora, Streptosporangium, Nocardia, Dactylosporangium, Microtetraspora and Thermomonospora on the plate, while restricting the development of true bacteria. The HV agar supported adequate growth and good sporulation for these actinomycetes.Even when spore suspensions were used as the inoculum, the HV agar produced remarkably larger numbers of actinomycetes, especially strains of the genera Micromonospora, Microbispora, Streptosporangium, Dactylosporangium and Saccharomonospora, than did glycerol-arginine agar. It was found that the spores of these actinomycetes were activated upon germination by treatment at 20°C for 30 min with a O.2% solution of humic acid prior to incubation.     

免疫磁珠富集技术联合选择性培养基快速检测单增李斯特菌

单增李斯特菌是一种危害极大的食源性致病菌,建立快速及特异的检测方法对于食品安全监控尤为重要。文中联合免疫磁珠与选择性培养基对不同浓度(101~105CFU/mL)单增李斯特菌进行检测,并对3种李斯特菌、金黄色葡萄球菌及副溶血弧菌进行交叉试验;同时模拟食物污染,探索免疫磁珠-平板法检测样品的检测限以及该方法的最快检测时间。结果显示特异性免疫磁珠联合选择性平板法可检出浓度为103CFU/mL及以上的单增李斯特菌;牛奶样品仅需6 h增菌能被检出,检测限为0.7 CFU/mL。联合使用免疫磁珠富集技术与选择性培养基,能在30 h内完成对牛奶样品的检测,较国标法减少38 h以上,且具有同等的灵敏度。     

Performance of a new chromogenic plating medium for the isolation of Listeria monocytogenes from marine environments

AIMS: This study investigated the performance of a new chromogenic plating medium for the detection of Listeria monocytogenes from naturally contaminated samples obtained from marine environments in Morocco in comparison with the conventional plating media PALCAM and Oxford. METHODS: A total of 479 marine samples (sea water, sediment and mussels) were collected from 16 littoral sites in the region of Agadir (western centre of Morocco). They were examined for the presence of L. monocytogenes using a slight modification of the standardized French method (AFNOR V 08-055) for the detection of L. monocytogenes from food and three different isolation media: PALCAM, Oxford and a new chromogenic plating medium. RESULTS AND SIGNIFICANCE OF THE STUDY: The Oxford and the new chromogenic plating media were found relatively more efficient than the PALCAM medium for the isolation of L. monocytogenes (chi-square test, P < 0.05) from marine samples. However, the new chromogenic plating medium was significantly more selective for L. monocytogenes (P < 0.005) than the two other isolation media as 87.5% of the suspect colonies on this medium were indeed confirmed through identification of the isolates vs 12.7% for Oxford and only 3.8% for the PALCAM medium.     

Czapek-Dox agar containing iprodione and dicloran as a selective medium for the isolation of Fusarium species

A new selective medium for Fusarium species has been developed using Czapek-Dox agar (CZ) containing the fungicides iprodione (3 mg/1) and dicloran (2 mg/1). This new medium (CZID) is selective against numerous species of Alternaria, Epicoccum, Penicillium and mucoraceous fungi. CZID was compared with CZ using samples of barley, malt, sorghum, bean and pea. Fusarium species produced large and easily recognizable colonies on CZID while isolates of Alternaria, Epicoccum and Rhizopus were significantly restricted on CZID compared with their growth on CZ. The use of CZID thus facilitates the isolation and subculturing of Fusarium species.     

Dry selective culture medium for isolation of streptococci (streptococcal broth)

Culture medium--dry rich broth for isolation of streptococci--is developed. It is characterized by good growth of microorganisms, accumulative effect and prominent inhibiting influence on growth of associated microorganisms. During growth of streptococci on the medium their main biological characteristic did not change. It has been shown that streptococcal broth provided isolation of streptococci in pure culture from clinical specimens.     

Development of a synthetic minimal medium for Listeria monocytogenes

A defined solid and liquid minimal medium, HTM, which contained methionine and cysteine as the sole amino acids, was developed for Listeria monocytogenes. Complex broth-grown L. monocytogenes had to adapt to HTM by inducing amino acid biosyntheis. HTM is the simplest minimal medium available for growth of L. monocytogenes.